Electronic olfactory sensors, with high sensitivity and specificity, can play a vital role in diagnosing chemo-sensory disorders, biomedical sciences, monitoring industrial processes, and safety. Fluorescence based olfactory sensors offer stable calibration, in-vivo operation, radiation hardness, and high information content. However, miniaturizing the sensor decreases the optical signal and any attempts to reduce the optical background may further decrease the optical signal. New innovative detectors are needed to detect extremely low light levels. Based on recent advances on micro-Avalanche Photodiode (muAPD) arrays at RMD, Inc. and olfactory sensors investigated at Tufts University, School of Medicine, we propose to develop a novel, high sensitivity, low power, olfactory sensor. The sensor will consist of an array of optical fibers, labeled with specific fluorophores, and will use chemically induced fluorescence temporal evolution to generate the chemical's specific signature. We will use an innovative total reflection technique to effectively quench the excitation light background. The fluorescence light will be detected by a muAPD array with single-photon sensitivity, 10/9 internal gain, and very low power requirements. In Phase I we propose to investigate candidate fluorophore - muAPD detector architectures, combined methods to decrease the optical excitation background, and to evaluate the prototype olfactory sensor performance. PROPOSED COMMERCIAL APPLICATION: The integration of mAPD technology into the new sensor offers the possibility of low cost, high sensitivity, portable, olfactory sensors and will extend the accuracy and range of medical diagnostic systems. Low cost olfactory sensors will find widespread applications in chemical and biological defense, explosives and drugs detection, as well as in the food industry, household products, industrial waste remote monitoring, perfumery, pharmaceuticals, bio-medicine, and tele-surgery.